The two unknown variables of the Thomas equation, constant of Thomas model and equilibrium uptake capacity, were determined using the plot ln (Co/Ci 1) against t (linear system form of the Thomas model). Table 3 shows the calculated values of the various parameters of the model, as well as the R². According to Table 9, the values of uptake capacity grow as the inlet As (III) concentration and bed height rise, while the values of constant of Thomas model fall, whereas the values of q_o and k_Th grew when the flow rate increased. Despite the fact that the Thomas model shows certain reasonable modifications for removal conditions, there is no clear connection in the breaking curve prediction. This can be seen in the disparities among experimental results and model-calculated uptake capacity estimates. Although the Thomas model is among the most frequently used to define the behaviour of biosorption process in column operations, its primary constraint is that it is rooted on second-order kinetics and assumes that biosorption is controlled by interfacial mass transfer rather than the chemical reaction. When this approach is employed to represent biosorption systems under specific circumstances, this mismatch can lead to inaccuracies (López-Cervantes et al. 2018).